X‐Ray crystallographic analysis of a ternary intercalation complex between proflavine and the dinucleoside monophosphates CpA and UpG

We report the crystal‐structure analysis of a complex involving the drug proflavine and the two dinucleoside monophosphates cytidylyl‐3′,5′‐adenosine (CpA) and uridylyl‐3′,5′‐guanosine (UpG). The planar drug molecule is intercalated between C ⃛G and U ⃛A Watson‐Crick base pairs, in a double‐helical fragmentlike arrangement. Sugar conformations at the 3′‐ends of the two strands are dissimilar. The backbone conformations fall within the ranges of values noted previously for dinucleoside intercalation complexes, and some correlations involving these are noted. The separation of the two strands and the basic twist angle of 16°, compared to other reported complexes, are indicative of sequence‐dependent effects of the drug binding.